1. Field of the Invention
The invention is based on a sensor arrangement for determining gas components and/or gas concentrations of gas mixtures of the generic type of the main claim.
2. Description of the Related Art
Sensors for determining the content of carbon monoxide in gas mixtures on the basis of semiconducting metal oxides which at high temperatures, as a function of the carbon monoxide content, but also of the oxygen content, change in electroconductivity are known (German Patent 2603785). One metal oxide used is, for example, tin oxide which at elevated temperatures adsorbs oxygen at its surface and ionizes it negatively. As a result, a potential threshold is formed on the grain boundaries of the tin oxide, which threshold grows with increasing concentration of the oxygen adsorbed in ionic form. If the tin oxide surface covered with oxygen then comes into contact with oxidizable gases such as, for example, CO, these are oxidized by the adsorbed oxygen. In the process, the negative charge at the interface and thus the potential threshold is lowered. The surface conductivity of the metal oxide therefore rises again. If the conductivity change is to be utilized for measuring the concentration of oxidizable gas components such as, for example, CO, NO.sub.x and HC, there thus results an oxygen cross sensitivity. In addition, at low oxygen partial pressures and, in particular in association with high temperatures, irreversible reduction of the semi-conducting metal oxide and thus failure of the sensor occurs. Hereinafter, the gas components to be determined are denoted as pollutant components.